Signal-on fluorescent strategy based on RNA cleavage-inhibited catalytic hairpin assembly and photo-induced electron transfer for Pb2+ detection

A signal-on fluorescence biosensing strategy was developed by integrating GR-5 DNAzyme, catalytic hairpin assembly (CHA), photo-induced electron transfer (PET) between G-quadruplex (G4)/hemin DNAzyme and fluorophore. An oligonucleotide (cGRE), complementary to the enzyme strand (GRE), was applied to facilitate the separation of substrate strand (GRS) from GR-5 DNAzyme. The separated GRS acted as a trigger to initiate the CHA process and the formation of G4/hemin DNAzyme, resulting in the fluorescence quenching via PET. The Pb2+-responsive cleavage of GRS led to the suppression of the occurrence of CHA and the generation of G4/hemin DNAzyme, yielding the enhancement of the fluorescence. This DNAzymes-CHA-PET Pb2+ assay can be carried out in a single tube, endowed with the obvious advantages of facile design, simple procedure and excellent specificity. The quantitative determination of Pb2+ was achieved in a broad range of 0.1–150 ng mL−1 with the detection limit of 0.03 ng mL−1. This strategy was successfully applied to the analysis of standard reference materials (drinking water), spiked water and fish samples. The ingenious design proposed herein provides a new method for routine screening of heavy metals, and also opens up new avenues for the development and application of PET biosensors based on G4/hemin DNAzyme.